In recent years, each of the devices constituting liquid crystal display apparatuses has been required to have high reliability and durability with increasing applications and functions of liquid crystal display apparatuses. For example, when a light source having a large quantity of light is used as in a transmissive liquid crystal projector, a polarization conversion element that converts natural light emitted from the light source to linearly polarized light receives strong radiation. Therefore, when the polarization conversion element has low durability, an illumination efficiency is decreased.
A polarization conversion element generally includes a polarizing-beam splitter array in which polarizing-beam splitters each having a polarization separation film and prisms each having a reflecting film are alternately bonded to each other, and a retardation plate is selectively provided on the outgoing surface of each of the polarizing-beam splitters.
Usual polarization conversion elements often use a UV (ultraviolet) curing-type adhesive as an optical adhesive for alternately bonding polarizing beam splitters and prisms to each other. Similarly, a UV curing-type adhesive is frequently used for bonding a ½ wavelength plate to the outgoing surface of each of the polarizing beam splitters.
However, polarization conversion elements using a UV curing-type adhesive quickly deteriorate with heat and light due to higher brightness of recent transmissive liquid crystal projectors and the like, thereby causing a problem with durability. For example, when burning occurs at a coating position in association with deterioration of the UV curing-type adhesive in a polarization conversion element, irradiation light is concentrated at the burning position, thereby causing a concern about a decrease in transmittance and the breakage of the element due to a high temperature.
In addition, in general, a dichroic retardation plate including a film containing an iodine-based or dye-based polymer organic material is frequently used as the retardation plate selectively provided on the outgoing surface of each of the polarizing beam splitters. A method used as a general method for producing a dichroic retardation plate includes dyeing a polyvinyl alcohol-based film with a dichroic dye such as iodine, cross-linking the film with a cross-linking agent, and then uniaxially stretching the film. The retardation plate including the polymer stretched film easily deteriorates with heat and UV light and thus has low durability. Also, since the retardation plate includes the polymer stretched film formed by stretching, this type of retardation plate generally easily contracts. In addition, the polyvinyl alcohol-based film uses a hydrophilic polymer and is thus easily deformed, particularly, under humidified conditions, and the mechanical strength as a device is weakened. Although a retardation element having an inorganic optical single crystal such as quartz or the like may be used for solving the problem, there is the problem of difficulty in increasing the size and of high raw material cost and processing cost.